Digital imaging systems typically utilize one or more sensors having an array of photodetectors. Each photodetector is associated with an image pixel. Color imagers generally employ photodetector arrays in which a color filter is fabricated over each photodetector. The wavelength range of each color filter varies according to the position of the photodetector in the array. For example, in imaging systems utilizing red-green-blue (RGB) color data, each photodetector has a red, green or blue filter so that only optical energy within the wavelength band passed by the filter is detected. FIG. 1 illustrates a Bayer filter pattern used in many conventional color cameras providing RGB image data. Each photodetector 14 in a group of pixels 10 generates a photocurrent responsive to the optical power incident on the photodetector and in the wavelength band of a corresponding color filter. Thus red photodetectors generate a photocurrent responsive to red light, green photodetectors generate photocurrent responsive to green light, and blue photodetectors generate photocurrent responsive to blue light. For example, a blue pixel 14 within the group of pixels 10 can only record an analog value for blue incident light. To produce an RGB value for the blue pixel 14, the blue value measured by the pixel is coupled with an average of the surrounding red values from adjacent red pixels and the average of the surrounding green values from adjacent green pixels.
Using multiple photodetectors in the image plane to generate an RGB value results in color artifacts and diminished color clarity. Image capture sensors have been developed which rely on the variation in the absorption coefficient of a sensor material as a function of wavelength. More specifically, the sensors are based on the variation in the penetration depth of light as a function of wavelength. For example, a detector structure has been developed in which three vertically stacked photodetectors are used to detect three colors. Each photodetector is fabricated with a certain thickness and doping concentration. The photodetector nearest the surface of the structure senses blue light, the photodetector in the middle of the stack senses green light, and the photodetector at the greatest depth from the surface senses red light. Optical filtering is employed to improve discrimination of the blue, green and red detection bands. Advantageously, each RGB pixel is defined by a single photodetector stack and, therefore, higher image quality is achieved; however, the sensor design is complex and optimized only for one set of wavelength bands. Moreover, such sensors require expensive manufacturing processes capable of fabricating tightly controlled layer thicknesses and doping concentrations necessary to achieve sensitivity to the three defined wavelength bands.